A Robust Cross-Regulation-Suppressed Single-
Inductor Multiple-Output DC-DC Converter with
Duty-Regulated Comparator Control
Yanqi Zheng
*‡†
, Marco Ho
*
, Ka Nang Leung
*
, Jianping Guo
‡†
and Hua Chen
#
Email: {yqzheng, mho, knleung}@ee.cuhk.edu.hk guojp3@mail.sysu.edu.cn
*
Department of Electronic Engineering, The Chinese University of Hong Kong, Hong Kong SAR, China
‡
School of Physics and Engineering, Sun Yat-sen University, Guangzhou, China
†
SYSU-CMU Shunde International Joint Research Institute, Foshan, China
#
Department of Electrical, Computer and Energy Engineering, University of Colorado Boulder, Boulder, Colorado, 80309
Abstract—A robust cross-regulation-suppressed single-
inductor multiple-output (SIMO) dc-dc converter with duty-
regulated comparator control is proposed. The control scheme
effectively combines comparator-based and linear-compensator-
based controllers to achieve fast load-transient response and low
cross regulation to other output channels simultaneously. The
control algorithm does not rely on duty-inductor-current feed-
forward which is sensitive to the accuracy of inductor-current
sensor. As a result, it can provide robust cross-regulation
suppression for a wide range of loading for the SIMO dc-dc
converter. Moreover, together with the average-inductor-current
control, the proposed control algorithm is suitable for SIMO dc-
dc converter which has auto-buck-boost property for each sub-
converter, which makes the SIMO converter suitable for
dynamic voltage scaling applications.
Keywords— Auto buck-boost, comparator based, current mode,
cross regulation, single-inductor multiple-output dc-dc converter.
I. INTRODUCTION
Single-inductor multiple-output (SIMO) dc-dc converter is
a potential solution for applications requiring multiple supplies
where the output voltages and power for each supply are
largely different [1]. In the past decade, some works were
reported to solve different problems and to improve the various
performances of a SIMO dc-dc converter [1]–[9]. To alleviate
the limitation of output power in the discontinuous conduction
mode (DCM) operation, pseudo-DCM and freewheeling
feedback technique were proposed [1], [2]. To reduce cross
regulation (CR), charge balanced method [3], [4], time-limited
power distribution [5], and small-signal parameter fitting [9]
were reported. To improve the transient speed, comparator-
based control algorithm has been adopted [6], [7]. To enable
dynamic voltage scaling (DVS) for SIMO dc-dc converter,
buck-boost technique is used [8]. By considering the
differences of the inductor current during operation, SIMO dc-
dc converters are usually classified into two types: time-
multiplexing control (TMC) and ordered power-distributive
control (OPDC). There are tradeoffs between power efficiency
and cross regulation. With different voltage controllers, SIMO
dc-dc converter can also be sorted into compensator-based and
comparator-based controls. Similar to the single-output dc-dc
converter, compensator-based control has lower transient speed
while comparator-based one suffers from switching noise and
voltage ripples.
In this paper, a SIMO dc-dc converter with proposed duty-
regulated comparator control (DRCC), which effectively
combines both the comparator-based and linear-compensator-
based controllers, is developed. With the proposed DRCC
method, not only cross regulation is suppressed, but the design
is also independent of both the accuracy of current sensor and
loading condition of each channel. Moreover, there is no
operation-frequency variation as in the comparator-based
controller. Hence, no phase-locked loop circuit is required.
II. C
ROSS REGULATION IN SIMO DC-DC CONVERTER
Cross regulation is a special issue in SIMO dc-dc converter
design. The origin of this problem can be described using Fig.
1, which shows the inductor current (i
L
) of a single-inductor
dual-output (SIDO) dc-dc converter. After a step of load
change is applied to Channel 1, the duty cycle for each channel
will be re-arranged. The criterion for no cross regulation to
Channel 2 is that i
LA
(1)·D
2
(1) = i
LA
(n)·D
2
(n), provided that
inductor current ripple is ignorable; otherwise, CR appears and
Channel 2 contains undershoots or overshoots. This can be
eliminated by duty-inductor-current feed-forward such as
charge balance [3], [4]. It can be observed that the duty cycle
of a channel can be expressed as
/
cLA
Dii
(1)
The work described in this paper was partly supported by grants from the
Research Grant Council of Hong Kong SAR Government under project
number CUHK 414210, and by a grant from National Natural Science
Foundation of China under 61204035.
i
L
T
s
t
io1
2T
s
nT
s
(n+1)T
s
t
D
1
(1) D
2
(1)
D
1
(n) D
2
(n)
i
LA
(1)
i
LA
(n)
…..
Q
1
(1) Q
2
(1)
Q
1
(n) Q
2
(n)
Fig. 1. Origin of cross regulation in SIMO dc-dc converter.